Combustion chemical vapor deposition (combustion CVD) is a relatively new technique for the growth of coatings. Combustion CVD is described, for example, in U.S. Pat. Nos. 5,652,021; 5,858,465; and 6,013,318, each of which is hereby incorporated herein by reference in its entirety.
Conventionally, in combustion CVD, precursors are dissolved in a flammable solvent and the solution is delivered to the burner where it is ignited to give a flame. Such precursors may be vapor or liquid and fed to a self-sustaining flame or used as the fuel source. A substrate is then passed under the flame to deposit a coating.
There are several advantages of combustion CVD over traditional pyrolytic deposition techniques (such as CVD, spray and sol-gel, etc.). One advantage is that the energy required for the deposition is provided by the flame. Another advantage is that combustion CVD techniques do not necessarily require volatile precursors. If a solution of the precursor can be atomized/nebulized sufficiently, the atomized solution will behave essentially as a gas and can be transferred to the flame without requiring an appreciable vapor pressure from the precursor of interest.
It will be appreciated that combustion deposition techniques may be used to deposit metal oxide coatings (e.g., singly-layer anti-reflective coatings) on glass substrates, for example, to alter the optical properties of the glass substrates (e.g., to increase visible transmission). To this end, conventional combustion deposition techniques were used by the inventors of the instant application to deposit a single layer anti-reflective (AR) film of silicon oxide (e.g., SiO2 or other suitable stoichiometry). The attempt sought to achieve an increase in light transmission in the visible spectrum (e.g., wavelengths of from about 400-700 nm) over clear float glass with an application of the film on one or both sides. The clear float glass used in connection with the description herein is a low-iron glass known as “Extra Clear,” which has a visible transmission typically in the range of 90.3% to about 91.0%. Of course, the examples described herein are not limited to this particular type of glass, or any glass with this particular visible transmission.
The combustion deposition development work was performed using a conventional linear burner with 465 holes even distributed in 3 rows over an area of 0.5 cm by 31 cm (155 holes per row). By way of example and without limitation, FIG. 1a shows a typical linear burner, and FIG. 1b is an enlarged view of the holes in the typical linear burner of FIG. 1a. As is conventional, the linear burner was fueled by a premixed combustion gas comprising propane and air. It is, of course, possible to use other combustion gases such as, for example, natural gas, butane, etc. The standard operating window for the linear burner involves air flow rates of between about 150 and 300 standard liters per minute (SLM), using air-to-propane ratios of about 15 to 25. Successful coatings require controlling the burner-to-lite distance to between about 10-50 mm when a linear burner is used.
Typical process conditions for successful films used a burner air flow of about 225 SLM, an air-to-propane ratio of about 19, four passes of the substrate across the burner, a burner-to-lite distance of 35 mm, and a glass substrate velocity of about 50 mm/sec.
FIG. 2 is a simplified view of an apparatus 200 including a linear burner used to carry out combustion deposition. A combustion gas 202 (e.g., a propane air combustion gas) is fed into the apparatus 200, as is a suitable precursor 204 (e.g., via insertion mechanism 206, examples of which are discussed in greater detail below). Precursor nebulization (208) and at least partial precursor evaporation (210) occur within the apparatus 200. The precursor could also have been delivered as a vapor reducing or even eliminating the need for nebulization The flame 18 may be thought of as including multiple areas. Such areas correspond to chemical reaction area 212 (e.g., where reduction, oxidation, and/or the like may occur), nucleation area 214, coagulation area 216, and agglomeration area 218. Of course, it will be appreciated that such example areas are not discrete and that one or more of the above processes may begin, continue, and/or end throughout one or more of the other areas.
Particulate matter begins forming within the flame 18 and moves downward towards the surface 26 of the substrate 22 to be coated, resulting in film growth 220. As will be appreciated from FIG. 2, the combusted material comprises non-vaporized material (e.g., particulate matter), which is also at least partially in particulate form when coming into contact with the substrate 22. To deposit the coating, the substrate 22 may be moved (e.g., in the direction of the velocity vector). Of course, it will be appreciated that the present invention is not limited to any particular velocity vector, and that other example embodiments may involve the use of multiple apparatuses 200 for coating different portions of the substrate 22, may involve moving a single apparatus 200 while keeping the substrate in a fixed position, etc. The flame 18 is about 10-50 mm from the surface 26 of the substrate 22 to be coated.
Unfortunately, the heat flux produced during combustion deposition creates a significant increase in substrate temperature. Also, heat is delivered to a smaller area (e.g., in comparison to the IR burners of certain example embodiments described below) causing much larger temperature gradients. Furthermore, the substrate temperature increases with smaller burner-to-lite distances and increasing numbers of passes. For example, using the process conditions identified above, the back side of the substrate was found to reach a temperature of 162° C. This equates to a linear estimate of temperature rate of rise of 71° C./burner/m/min.
The substrate temperature extremes and resultant thermal gradient experienced by the glass during deposition leads to stress changes in the glass. This phenomenon, in turn, has resulted in spontaneous glass fracture during coating, in post-coating cooling, and/or in subsequent deposition of the same film on the opposite side of the lite. Additionally, the glass experiences bowing, which ultimately leads to coating uniformity issues.
Thus, it will be appreciated that there is a need in the art for combustion deposition techniques that overcome one or more of these and/or other disadvantages, and/or improved techniques for depositing metal oxide coatings (single layer anti-reflective coatings) on glass substrates via combustion deposition.
In certain example embodiments of this invention, a method of forming a coating on a glass substrate using combustion deposition is provided. A glass substrate having at least one surface to be coated is provided. A reagent (and optionally, a carrier medium) is selected, and if a carrier medium is used, the reagent and the carrier medium are mixed together to form a reagent mixture. The reagent is selected such that at least a portion of the reagent is used in forming the coating. A precursor to be combusted with the reagent (or reagent mixture) is introduced. Using at least one infrared burner, at least a portion of the reagent (or reagent mixture) and the precursor are combusted to form a combusted material, with the combusted material comprising non-vaporized material. The glass substrate is provided in an area so that the glass substrate is heated sufficiently to allow the combusted material to form the coating, directly or indirectly, on the glass substrate.
In certain example embodiments, a fuel gas and oxygen source are selected and mixed together to form a combustion gas mixture. At least a portion of the combustion gas mixture is used in forming the coating. A precursor is selected such that at least a portion of the combustion products form a coating with desired properties. The precursor is introduced into the combustion gas stream to form a reagent mixture. Using at least one infrared burner, at least a portion of the reagent mixture is reacted via combustion to form reaction products, with at least a portion of the reaction products comprising non-vaporized material.
In certain example embodiments, a method of applying a coating to a substrate using combustion deposition is provided. A substrate having at least one surface to be coated is provided. A reagent (and optionally, a carrier medium) is selected, and if a carrier medium is selected, the reagent and the carrier medium are mixed together to form a reagent mixture, with the reagent being selected such that at least a portion of the reagent forms the coating. A precursor to be combusted with the reagent (or reagent mixture) is introduced, with the precursor including silicon. Using at least one infrared burner, at least a portion of the reagent (or reagent mixture) and the precursor are combusted to form a combusted material. The substrate is provided in an area so that the substrate is heated sufficiently to allow the combusted material to form the coating, directly or indirectly, on the substrate. The deposited coating comprises silicon oxide. The coating increases visible transmission of the glass substrate by at least about 1.7%.
In certain example embodiments, a method of applying a coating to a substrate using combustion deposition is provided. A substrate having at least one surface to be coated is provided. A reagent (and optionally, a carrier medium) is selected, and if a carrier medium is selected, and the reagent and the carrier medium are mixed together to form a reagent mixture, with the reagent being selected such that at least a portion of the reagent forms the coating. A precursor to be combusted with the reagent (or reagent mixture) is introduced, with the precursor including silicon. Via IR radiation from an IR radiation source, the IR radiation having a wavelength of about 2.5-3.5 microns distributed substantially two-dimensionally, at least a portion of the reagent (or reagent mixture) and the precursor are combusted to form a combusted material, the combusted material comprising non-vaporized material. The glass substrate is provided in an area about 2-5 mm from IR radiation source so that the glass substrate is heated sufficiently to allow the combusted material to form the coating substantially uniformly, directly or indirectly, on the glass substrate. The coating is substantially uniform.
In certain example implementations, the substrate temperature is heated to a temperature lower than that of conventional CVD and/or a lower temperature flame is used to combust the material to be combusted. In certain example implementations, the coating may be applied in a substantially uniform manner (e.g., across two dimensions), as measured by variations in thickness of the coating (e.g., with variations not exceeding about ±10%) and/or variations in the visible transmission gain (e.g., with variations in either percent transmission or percent transmission gain not exceeding about ±0.5%).
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.